Using unstable nitrides to form semiconductor structures

ABSTRACT

Incompatible materials, such as copper and nitrided barrier layers, may be adhered more effectively to one another. In one embodiment, a precursor of copper is deposited on the nitrided barrier. The precursor is then converted, through the application of energy, to copper which could not have been as effectively adhered to the barrier in the first place.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application a continuation of U.S. patent application Ser. No.12/788,603, filed on May 27, 2010, which is a divisional of U.S. patentapplication Ser. No. 11/359,060, filed on Feb. 22, 2006,now patented asU.S. Pat. No. 7,749,906.

BACKGROUND

This invention relates generally to the fabrication of integratedcircuits.

In the fabrication of integrated circuits, it is desirable to use avariety of different materials over a variety of different substrates.Sometimes materials that an engineer would like to use over a givensubstrate are incompatible with that substrate. By “incompatible” it isintended to mean that the upper material cannot be deposited onto thelower layer with sufficient adherence to the lower layer to avoiddelamination.

Thus, commonly, in order to adhere these incompatible layers to oneanother, special deposition techniques are required or adhesion layersmust be provided between the incompatible layers.

It is also desirable in a variety of applications to form nanowires orvery small electrical conductors in semiconductor integrated circuits.Commonly, the deposition of such small conductors is extremelydifficult. Moreover, to form a conductor, such as a copper conductorburied in other material, involves a large and cost ineffective numberof process steps.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an enlarged, cross-sectional view at an early stage ofmanufacture according to one embodiment;

FIG. 2 is an enlarged, cross-sectional view at a subsequent stage ofmanufacture according to one embodiment;

FIG. 3 is an enlarged, cross-sectional view at a stage subsequent to thestage shown in FIG. 1 according to one embodiment;

FIG. 4 is an enlarged, cross-sectional view at a subsequent stage toFIG. 3 in accordance with one embodiment of the present invention;

FIG. 5 is an enlarged, cross-sectional view of another embodiment of thepresent invention; and

FIG. 6 is an enlarged, cross-sectional view of still another embodimentof the present invention.

DETAILED DESCRIPTION

Referring to FIG. 1, a layer of a first material 12, over a substrate orwafer 10, may receive on its upper surface a deposit of a secondmaterial 14. The material 14 and the material 12 may be sufficientlycompatible that adequate adherence can be obtained between the materials12 and 14 in some embodiments. However, the material 14, now adhered tothe material 12, may then be converted to another material incompatiblewith the material 12 if directly deposited on the material 12. Bydepositing the material 14 in a first form and then converting it into asecond form, the incompatible material may be successfully adhered tothe first material 12.

As an example, the material 12 may be a nitrided barrier layer such astitanium nitride or tungsten nitride. The material 14, in oneembodiment, may be an unstable metal nitride, such as Cu₃N or Cu₄N, astwo examples. As another example, the material 14 may be Ni₃N.

In one embodiment, the material 14 is deposited by a atomic layerdeposition (ALD) and/or chemical vapor deposition (CVD). Precursors maybe used to deposit the unstable metal nitrides by ALD or CVD, including,but not limited to, copper amidinate variants, betadiketiminates,azaallyls, betadiketonates, pyridines, cyclic arenes, and alkenes.Deposition of the material 14 may take place at a substrate temperaturebetween 80° C. and 150° C., under chamber pressures between 100 mTorr to10 Torr, in some embodiments. Co-reactants may be pulsed or flown toform unstable metal nitrides such as Cu₃N or Cu/Cu₃N mixtures. Theco-reactants may include, but are not limited to, NH₃, primary amines,secondary amines, tertiary amines, hydrazine, BR3-amine adducts (where Ris alkyl, proton or both and the amine is primary, secondary, tertiary),azides, as well as pure nitrogen, nitrogen plasma, or N₂/H₂ plasma, aswell as any plasma and combinations from aforementioned chemicals.

Then, referring to FIG. 2, the material 14 may be decomposed to form apure or substantially nitride free metal layer 16. After deposition ofon patterned wafers, the layer 16 is decomposed to pure copper, in oneembodiment, or pure nickel, in another embodiment, where Ni₃N is used.Methods for decomposing the material 14 include thermal annealing inpure hydrogen gas, diluted hydrogen gas in an inert gas, annealing inNH₃ or nitrogen gas, at temperatures ranging from 200° C. to 500° C.,for times ranging between five minutes to 120 minutes. The Cu₃N material14 may transform into near bulk copper conductivity within about onehour.

In another embodiment, an electron beam, with appropriate diameter andenergy, may be used to decompose the Cu₃N into copper. Other thermaldecomposition techniques may be used, including rapid thermal annealingin vacuum and joule heating using a resistive underlayer. Non-thermaldecomposition may also be used, including ion implantation, ionbombardment, light, and plasma (remote and near) annealing.

In some embodiments, as shown in FIG. 3, the material 14 may beconverted entirely into a pure metal layer 16. In other embodiments, asshown in FIG. 2, the conversion may be incomplete, leaving a thin layerof material 14 between the pure metal layer 16 and the material 12.Thus, the material 14 remains in contact with the first material 12 overa substrate 10, such as a silicon substrate.

The material 14 may serve as an adhesion layer to the nitrided barriermaterial 12. The conversion of the material 14 allows the deposition oftwo consecutive ALD or CVD layers for barrier and seed, all in onedeposition step in some embodiments.

The presence of a nitrided barrier material 12 may also act as agetterer of nitrogen and may not allow the formation of CuN layers inthe pure copper film. A preferred embodiment uses ALD TaN as thenitrided barrier with Cu-nitride deposition. In addition, the Cu₃Nmaterial may be deposited directly on silicon or carbon doped silicon toform SiCN, which may act as a barrier to copper diffusion. In stillanother embodiment, the Cu₃N layer is deposited on porous low dielectricconstant material and can serve as a dual sacrificial poresealing/adhesion layer.

Referring to FIG. 4, in some embodiments, a Cu₃N layer 14 a may be usedas a sacrificial/morphing non-reflective coating on a copper metal layer16 to permit further patterning using optical techniques. In such case,a Cu₃N layer 14 a may first be deposited and post-treated to pure coppermetal layer 16, as indicated in FIG. 3. Then a second Cu₃N layer 14 amay be deposited over the reflective metal layer 16. The Cu₃N layer 14 aacts as a non-reflective layer for patterning an overlying resist andetching. After the patterning is complete, the Cu₃N layer 14 a can actas an adhesion layer or be reverted back to a conductive or pure metallayer.

In a further embodiment, copper and Cu₃N may be used as selectiveetching layers, or Cu₃N can be selectively etched over copper to produceconductive copper lines.

Moving to FIG. 5, in accordance with one embodiment of the presentinvention, an atomic layer deposition metal nitride material 14 may beformed over a nitrided barrier material 12 on top of a substrate 10,such as a silicon substrate. The material 14 may be selectivelyconverted into pure or substantially nitride free copper metal strip 16a by the use of an electron beam E or other methods already mentioned. Anano-patterned metal strip 16 a, shown in FIG. 6, may be obtained byplacing the nanometer sized (i.e., of a width on the order of abillionth of a meter) electron beam E at exact locations using a reticleor precise beam location. For example, a nanowire may be formed bymoving the electron beam over the material 14. The surroundingunconverted dielectric material 14 can be used as an encapsulatingmaterial to avoid line shorting.

In some embodiments of the present invention, it is possible to depositfilms with precise thickness and composition control. The deposition ofconformal, uniform, and nanometer-sized films may be achieved in someembodiments with a nitrided cap and sidewalls to prevent full lineoxidation. Conductive lines or layers may be precisely located in somecases and improved adhesion to silicon or nitrided substrates may beachieved. Also, low reflectivity enabling patterning may be accomplishedin some cases. In some embodiments, deposition and patterning ofultra-thin lines may be achieved with width and height less than tennanometers or to a size enabled by electron beams or scanning tunnelingmicroscopy (STM) resolution.

References throughout this specification to “one embodiment” or “anembodiment” mean that a particular feature, structure, or characteristicdescribed in connection with the embodiment is included in at least oneimplementation encompassed within the present invention. Thus,appearances of the phrase “one embodiment” or “in an embodiment” are notnecessarily referring to the same embodiment. Furthermore, theparticular features, structures, or characteristics may be instituted inother suitable forms other than the particular embodiment illustratedand all such forms may be encompassed within the claims of the presentapplication.

While the present invention has been described with respect to a limitednumber of embodiments, those skilled in the art will appreciate numerousmodifications and variations therefrom. It is intended that the appendedclaims cover all such modifications and variations as fall within thetrue spirit and scope of this present invention.

1. A semiconductor structure comprising: a semiconductor substrate; alayer of metal nitride including at least three metal atoms per nitrogenatom; and a layer of the pure metal over said metal nitride.
 2. Thestructure of claim 1 wherein said substrate includes a nitride material.3. The structure of claim 2 wherein said substrate includes a titaniumor tungsten nitride.
 4. The structure of claim 1 wherein said metal iscopper.
 5. A semiconductor structure comprising: a substrate; asubstantially nitride free metal layer over said substrate; and a metalnitride over said metal, said metal nitride including at least threemetal atoms per nitrogen atom.
 6. The structure of claim 5 wherein saidmetal is copper.
 7. The structure of claim 5 wherein said substrate is anitride.
 8. The structure of claim 7 wherein said substrate includestungsten or titanium nitride.
 9. A semiconductor structure comprising: asubstrate; a metal nitride layer over said substrate; and a region ofsubstantially nitride free metal formed in said layer.
 10. The structureof claim 9 wherein said metal nitride includes the same metal as saidsubstantially nitride free metal.
 11. The structure of claim 9 whereinsaid metal is elongated.
 12. The structure of claim 11 wherein saidmetal is a nanowire.